There has been a substantial amount of interest in the anticonvulsant and neuroprotective actions of dextromethorphan. Its therapeutic efficacy, however, is limited by its extensive first-pass elimination by way of the cytochrome P4502D6 enzyme in humans. The purpose of this research was to determine whether quinidine (a selective inhibitor of cytochrome P4502D6) could improve dextromethorphan systemic delivery in patients with amyotrophic lateral sclerosis (a neurodegenerative disease). In the absence of quinidine, 60 mg dextromethorphan every 12 hours resulted in plasma concentrations of only 12 +/- 13 ng/ml (range, less than 5 to 40 ng/ml; n = 7). The same dose of dextromethorphan in the presence of 75 mg quinidine every 12 hours resulted in dextromethorphan plasma concentrations of 241 +/- 94 ng/ml (range, 157 to 402 ng/ml; n = 5). The achievement of higher dextromethorphan plasma concentrations was also associated with an increased occurrence of adverse effects in some patients. Based on the brain/plasma ratio for dextromethorphan in rats, it is estimated that brain dextromethorphan concentrations of 1.0 to 10 micrograms/gm may be attainable in humans by inhibition of cytochrome P4502D6 activity with quinidine.

Background : Drug-induced QTc prolongation is becoming increasingly important in oncology since novel therapies result in prolonged survival of cancer patients already predisposed to cardiotoxicity. Methods : We review the challenges of implementing the ICH E14 guidance in oncology and propose an integrated approach to QTc risk assessment of nonadjuvant anticancer agents (NAAs), with quantitative outcome criteria. Results : We recommend informed use of non-clinical cardiac safety pharmacology results, some degree of robust ECG assessments in early phase studies, a dedicated QTc study in cancer patients conducted at the appropriate time pre-, peri-, or post-approval (with the design and timing agreed upon with regulatory agencies), and ECG monitoring in late-phase studies commensurate with the outcome of previous QTc studies. Conclusion : The proposed approach would facilitate risk-benefit assessment for NAAs during clinical development and regulatory review, and enable adequate labeling for safe and effective postmarketing use in cancer patients.

Delivery of CPT to the target tumor tissue is achievable by means of the MAG-CPT polymer-bound delivery system, with the equilibrium between plasma and tumor tissue concentrations of released CPT being established within 24 h after dosing. However, preferential retention of MAG-bound or released CPT in the tumor relative to normal tissue or plasma was not detected during the 7 days after dosing. The methods employed in our study could be of use in making "go/no-go" decisions on further development of anticancer drugs.

1 The phenotyping parameters for dextromethorphan and mephenytoin were assessed in 48 normal male volunteers following administration of each metabolic probe drug on separate occasions and together according to a randomized 3-way crossover design. 2 Neither the urinary S-/R-mephenytoin ratio nor the dextromethorphan metabolic ratio were altered significantly by coadministration of the probe drugs. 3 Five-hundred and nineteen subjects were screened for expression of mephenytoin 4-hydroxylase and dextromethorphan O-demethylase activity following the coadministration of mephenytoin and dextromethorphan. The activity was determined in each case by methods not requiring any quantitative measurements. 4 Nineteen (3.7%) of the subjects were identified as poor metabolizers (PMs) of mephenytoin and 35 subjects (6.7%) as PMs of dextromethorphan. 5 All PMs of dextromethorphan were confirmed by more rigorous evaluation of the metabolic ratio.